This a simple example of how to write a unit test which creates an injectable mock for a custom validator. It also mocks a custom validator faking that validation occurred.

Create an annotation for your custom validation

Create a constraint validator

Code the validator and include any dependencies you need

Next add an instance of LocalValidatorFactoryBean to your context

@Bean
public LocalValidatorFactoryBean validator() {
	return new LocalValidatorFactoryBean();
}

Create an instance of the validation annotation

@ValidUserName
private String userName;

Next create a test, auto wire in the Validator and add a mockito @MockBean containing the dependencies the validator requires

@Autowired
private Validator validator;

@MockBean
private IUserUtils userUtils;

Ensure your validator is in the configuration of the test

@ContextConfiguration(classes= {ValidationConfiguration.class})

Write your test while mocking the validators dependencies!